Electric heating for turbomachinery clearance control powered by hybrid energy storage system

ABSTRACT

A hybrid energy storage and control system for a clearance control system for a gas turbine engine may comprise a hybrid electric power source, a first converter, a second converter configured to receive electric power from the hybrid electric power source via the first converter and configured to send the electric power to a heating element for controlling a blade tip clearance between a rotor blade and an outer structure of the gas turbine engine, and a controller in electronic communication with the second converter. The hybrid electric power source may comprise a battery, a supercapacitor, and/or an ultracapacitor.

FIELD

The present disclosure relates to gas turbine engines, and morespecifically, to the management of turbomachinery clearances.

BACKGROUND

Gas turbine engines typically include a fan delivering air into acompressor. The air is compressed in the compressor and delivered into acombustion section where it is mixed with fuel and ignited. Products ofthis combustion pass downstream over turbine blades, driving them torotate. Turbine rotors, in turn, drive the compressor and fan rotors.The efficiency of the engine is impacted by ensuring that the productsof combustion pass in as high a percentage as possible across theturbine blades. Leakage around the blades reduces efficiency. Thus, ablade outer air seal (BOAS) is provided radially outward of the bladesto prevent leakage.

The BOAS is spaced from a radially outer part of the blade by a tipclearance. The BOAS is traditionally associated with a carrier elementthat is mounted to an engine case. Since the blades, the BOAS, and thestructure that support the BOAS are different sizes and/or are formed ofdifferent materials, they respond to temperature changes in differentmanners. As these structures expand at different rates in response totemperature changes, the tip clearance may be reduced and the blade mayrub on the BOAS, or the tip clearance may increase reducing efficiency,both of which are undesirable.

Clearance control systems are used to control the tip clearance underdifferent operational conditions. Traditional clearance control systemsutilize valves and manifolds to direct fan air to specific engine caselocations. The cooling air thermally shrinks the engine case at theselocations to improve tip clearance and thus fuel burn. However, thesemanifolds and valves are large, heavy, and expensive. These systems canalso be slow to respond and provide limited clearance improvement. Byfurther reducing tip clearances increasing engine efficiency demands canbe met.

SUMMARY

A clearance control system for a gas turbine engine is disclosed,comprising a rotor blade, an outer structure disposed radially outwardfrom the rotor blade, a heating element configured to cause the outerstructure to be heated in response to electric current being supplied tothe heating element, wherein a gap between the rotor blade and the outerstructure is at least one of increased, decreased, and maintained inresponse to the outer structure being heated, a hybrid electric powersource configured to supply the electric current to the heating element,and a controller configured to regulate the electric current beingsupplied to the heating element.

In various embodiments, the hybrid electric power source comprises atleast one of a battery, a supercapacitor, and an ultracapacitor.

In various embodiments, the clearance control system further comprises afirst converter in electronic communication with the battery and thecapacitor.

In various embodiments, the clearance control system further comprises asecond converter configured to receive DC power from the first converterand supply the heater element with electrical power.

In various embodiments, the second converter comprises a DC-AC inverterand the heating element is configured to cause the outer structure to beheated via induction heating.

In various embodiments, the clearance control system further comprises avalve assembly configured to meter a cooling air flow to the outerstructure.

In various embodiments, the controller is configured to at least one ofdecrease, maintain, or increase the gap by coordinating the cooling airflow and the electric current being supplied to the heating element.

In various embodiments, the controller coordinates the cooling air flowvia valve position control of the valve assembly.

In various embodiments, the controller is configured to send a firstcontrol signal to a power electronics for varying the electric currentsupplied to a heating element to cause the outer structure to move in afirst radial direction, and send a second control signal to the valveassembly for varying a cooling air flow supplied to the outer structureto cause the outer structure to move in a second radial direction,wherein the first radial direction is opposite the second radialdirection

A hybrid energy storage and control system for a clearance controlsystem for a gas turbine engine is disclosed, comprising a hybridelectric power source, a first converter, a second converter configuredto receive electric power from the hybrid electric power source via thefirst converter and configured to send the electric power to a heatingelement for controlling a blade tip clearance between a rotor blade andan outer structure of the gas turbine engine, and a controller inelectronic communication with the second converter.

In various embodiments, the hybrid electric power source comprises atleast one of a battery, a supercapacitor, and an ultracapacitor.

In various embodiments, the controller is configured to regulate theelectric power supplied to the heating element via the second converter.

In various embodiments, the first converter is configured to regulatepower between at least one of the battery, the supercapacitor, and theultracapacitor.

In various embodiments, the second converter comprises a DC-DCconverter, the heating element configured to heat up the outer structureby resistive heating.

In various embodiments, the second converter comprises a DC-AC inverter,the heating element configured to heat up the outer structure byinduction heating.

In various embodiments, the second converter comprises a AC-ACconverter, the heating element configured to heat up the outer structureby induction heating.

In various embodiments, at least one of the battery, the supercapacitor,and the ultracapacitor is configured to receive electric power from agenerator in response to the at least one of the battery, thesupercapacitor, and the ultracapacitor being depleted of electric powerby the heating element.

A method for active bi-directional control of an outer structure of agas turbine engine is disclosed, comprising sending, by a controller, afirst control signal to a power electronics for varying an electriccurrent supplied to a heating element to cause the outer structure tomove in a first radial direction, and sending, by the controller, asecond control signal to a valve assembly for varying a cooling air flowsupplied to the outer structure to cause the outer structure to move ina second radial direction, wherein the first radial direction isopposite the second radial direction.

In various embodiments, the method further comprises varying a blade tipclearance in response to the outer structure moving.

In various embodiments, the method further comprises receiving, by thecontroller, an electrical current value currently being supplied to theheating element, receiving, by the controller, a current valve position,determining, by the controller, a current blade tip clearance valuebased upon the electrical current value and the current valve position,and receiving, by the controller, a target blade tip clearance value,wherein the first control signal and the second control signal are basedupon the current blade tip clearance value and the target clearancevalue.

The forgoing features and elements may be combined in variouscombinations without exclusivity, unless expressly indicated hereinotherwise. These features and elements as well as the operation of thedisclosed embodiments will become more apparent in light of thefollowing description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed outand distinctly claimed in the concluding portion of the specification. Amore complete understanding of the present disclosure, however, may bestbe obtained by referring to the detailed description and claims whenconsidered in connection with the following illustrative figures. In thefollowing figures, like reference numbers refer to similar elements andsteps throughout the figures.

FIG. 1 illustrates a schematic representation of one example of a gasturbine engine, in accordance with various embodiments;

FIG. 2A illustrates a heating element coupled to an outer surface of anouter structure disposed radially outward from a blade for maintaining ablade tip clearance gap, in accordance with various embodiments;

FIG. 2B illustrates a heating element embedded in an outer structuredisposed radially outward from a blade for maintaining a blade tipclearance gap, in accordance with various embodiments;

FIG. 2C illustrates a cross-section view of a heating element spacedapart from an outer surface of an outer structure disposed radiallyoutward from a blade for maintaining a blade tip clearance gap, inaccordance with various embodiments;

FIG. 2D illustrates a cross section axial view of a heating elementembedded in an outer structure disposed radially outward from a bladefor maintaining a blade tip clearance gap, in accordance with variousembodiments;

FIG. 3A illustrates a schematic view of a hybrid electric power andcontrol system for a clearance control system for a gas turbine engine,in accordance with various embodiments;

FIG. 3B illustrates a schematic view of a hybrid electric power andcontrol system for a clearance control system for a gas turbine engine,in accordance with various embodiments;

FIG. 3C illustrates a schematic view of an active clearance controllogic comprising a clearance estimator and a control algorithm, inaccordance with various embodiments;

FIG. 4A and FIG. 4B illustrate a section view of a full hoop clearancecontrol ring and a BOAS assembly positioned between a blade and anengine case and an active clearance control system for controlling aposition of the BOAS via the clearance control ring, in accordance withvarious embodiments;

FIG. 5A and FIG. 5B illustrate a section view of a BOAS assemblypositioned between a blade and an engine case and an active clearancecontrol system for controlling a position of the BOAS via the enginecase, in accordance with various embodiments;

FIG. 6 shows an annular component (e.g., a clearance control ring or anengine case) at room temperature (middle), a decreased temperature(left), and an elevated temperature (right), in accordance with variousembodiments;

FIG. 7 shows a flow chart illustrating a method for activebi-directional control of an outer structure, in accordance with variousembodiments; and

FIG. 8 shows a flow chart illustrating a method for activebi-directional control of an outer structure, in accordance with variousembodiments.

Elements and steps in the figures are illustrated for simplicity andclarity and have not necessarily been rendered according to anyparticular sequence. For example, steps that may be performedconcurrently or in different order are illustrated in the figures tohelp to improve understanding of embodiments of the present disclosure.

DETAILED DESCRIPTION

The detailed description of exemplary embodiments herein makes referenceto the accompanying drawings, which show exemplary embodiments by way ofillustration. While these exemplary embodiments are described insufficient detail to enable those skilled in the art to practice thedisclosures, it should be understood that other embodiments may berealized and that logical changes and adaptations in design andconstruction may be made in accordance with this disclosure and theteachings herein. Thus, the detailed description herein is presented forpurposes of illustration only and not of limitation.

The scope of the disclosure is defined by the appended claims and theirlegal equivalents rather than by merely the examples described. Forexample, the steps recited in any of the method or process descriptionsmay be executed in any order and are not necessarily limited to theorder presented. Furthermore, any reference to singular includes pluralembodiments, and any reference to more than one component or step mayinclude a singular embodiment or step. Also, any reference to attached,fixed, coupled, connected or the like may include permanent, removable,temporary, partial, full and/or any other possible attachment option.Additionally, any reference to without contact (or similar phrases) mayalso include reduced contact or minimal contact. Surface shading linesmay be used throughout the figures to denote different parts but notnecessarily to denote the same or different materials.

As used herein, “distal” refers to the direction radially outward, orgenerally, away from the axis of rotation of a turbine engine. As usedherein, “proximal” refers to a direction radially inward, or generally,towards the axis of rotation of a turbine engine. As used herein, “aft”refers to the direction associated with a tail (e.g., the back end) ofan aircraft, or generally, to the direction of exhaust of a gas turbineengine. As used herein, “forward” refers to the direction associatedwith a nose (e.g., the front end) of the aircraft, or generally, to thedirection of flight or motion.

A clearance control system, as provided herein, may be useful gasturbine engines, including for use in the turbine section and/or in thecompressor section of the gas turbine engine, and may be useful for anyother suitable turbomachinery where rotor blade tip clearance control isdesirable.

A clearance control system, as provided herein, may include a heatingelement for transferring thermal energy to an outer structure to causethe outer structure to thermally grow (e.g., to move in a first radialdirection) and a valve assembly for regulating a cooling air flowdirected to the outer structure to cause the outer structure tothermally shrink (e.g., to move in a second radial direction). Activebi-directional control of the outer structure in both radial directionsmay allow for decreased response time (i.e., decrease time for thermalexpansion and/or contraction of the outer structure) and faster changesin blade tip clearance. A clearance control system, as provided herein,may allow for tighter tolerances manufactured into the system'scomponents due to increased response time of blade tip clearancecontrol.

In various embodiments, and with reference to FIG. 1, a gas turbineengine 120 is disclosed. Gas turbine engine 120 may comprise a two-spoolturbofan that generally incorporates a fan section 122, a compressorsection 124, a combustor section 126, and a turbine section 128. Gasturbine engine 120 may also comprise, for example, an augmenter section,and/or any other suitable system, section, or feature. In operation, fansection 122 may drive air along a bypass flow-path B, while compressorsection 124 may further drive air along a core flow-path C forcompression and communication into combustor section 126, beforeexpansion through turbine section 128. FIG. 1 provides a generalunderstanding of the sections in a gas turbine engine, and is notintended to limit the disclosure. The present disclosure may extend toall types of applications and to all types of turbine engines,including, for example, turbojets, turboshafts, and three spool (plusfan) turbofans wherein an intermediate spool includes an intermediatepressure compressor (“IPC”) between a low pressure compressor (“LPC”)and a high pressure compressor (“HPC”), and an intermediate pressureturbine (“IPT”) between the high pressure turbine (“HPT”) and the lowpressure turbine (“LPT”).

In various embodiments, gas turbine engine 120 may comprise a low speedspool 130 and a high speed spool 132 mounted for rotation about anengine central longitudinal axis A-A′ relative to an engine staticstructure 136 via one or more bearing systems 138 (shown as, forexample, bearing system 138-1 and bearing system 138-2 in FIG. 1). Itshould be understood that various bearing systems 138 at variouslocations may alternatively or additionally be provided, including, forexample, bearing system 138, bearing system 138-1, and/or bearing system138-2.

In various embodiments, low speed spool 130 may comprise an inner shaft140 that interconnects a fan 142, a low pressure (or a first) compressorsection 144, and a low pressure (or a second) turbine section 146. Innershaft 140 may be connected to fan 142 through a geared architecture 148that can drive fan 142 at a lower speed than low speed spool 130. Gearedarchitecture 148 may comprise a gear assembly 160 enclosed within a gearhousing 162. Gear assembly 160 may couple inner shaft 140 to a rotatingfan structure. High speed spool 132 may comprise an outer shaft 150 thatinterconnects a high pressure compressor (“HPC”) 152 (e.g., a secondcompressor section) and high pressure (or a first) turbine section 154.A combustor 156 may be located between HPC 152 and high pressure turbine154. A mid-turbine frame 157 of engine static structure 136 may belocated generally between high pressure turbine 154 and low pressureturbine 146. Mid-turbine frame 157 may support one or more bearingsystems 138 in turbine section 128. Inner shaft 140 and outer shaft 150may be concentric and may rotate via bearing systems 138 about enginecentral longitudinal axis A-A′. As used herein, a “high pressure”compressor and/or turbine may experience a higher pressure than acorresponding “low pressure” compressor and/or turbine.

In various embodiments, the air along core airflow C may be compressedby low pressure compressor 144 and HPC 152, mixed and burned with fuelin combustor 156, and expanded over high pressure turbine 154 and lowpressure turbine 146. Mid-turbine frame 157 may comprise airfoils 159located in core airflow path C. Low pressure turbine 146 and highpressure turbine 154 may rotationally drive low speed spool 130 and highspeed spool 132, respectively, in response to the expansion.

With combined reference to FIG. 2A, FIG. 2B, and FIG. 2C, an outerstructure 220 spaced by a clearance gap G from a radially outer tip of arotor blade 262, is illustrated, in accordance with various embodiments.Outer structure 220 may generally surround rotor blade 262 in a hoopstructure or a segmented hoop structure, as described herein in furtherdetail. In various embodiments, outer structure 220 may be similar tocontrol ring 66 as described with respect to FIG. 4A. In variousembodiments, outer structure 220 may be similar to engine case 570 asdescribed with respect to FIG. 5A. In various embodiments, the rotorblade 262 is a component of the turbine section 128 as shown in FIG. 1.In various embodiments, the rotor blade 262 is a component of thecompressor section 124 as shown in FIG. 1.

A heating element is generally shown at 210. In various embodiments, theheating element 210 may be coupled to an outer surface 222 of outerstructure 220 (FIG. 2A). Coupling the heating element 210 to an outersurface 222 may allow for ease of installation of the heating element210 onto outer structure 220 as well as accessibility to the heatingelement 210 when installed on the outer structure 220 (e.g., forinspection, repair, and/or replacement).

In various embodiments, the heating element 210 is embedded in the outerstructure 220 (FIG. 2B). Embedding the heating element 210 within theouter structure 220 may provide responsive, as well as evenlydistributed, heating to the outer structure 220.

In various embodiments, the heating element 210 is spaced apart from theouter structure 220 (FIG. 2C). Spacing apart heating element 210 fromthe outer structure 220 may allow heating element 210 and outerstructure 220 to move relative to each other without impartingmechanical stress therebetween (e.g., thermally induced stresses).Spacing apart heating element 210 from the outer structure 220 may beparticularly useful for induction heating applications, as describedherein.

The heating element 210 may be wired to an electric power source 205,for instance by way of wires 202 (i.e., leads, lead wires) on oppositesides of the heating element 210. Any appropriate type of arrangementsmay be used to allow a current supply through the heating element 210from the electric power source 205. Electric power source 205 may alsocomprise multiple circuits for instance in parallel to heat up theheating element 210 in segments.

A processor, such as controller 280 may regulate electric power sent toheating element 210. Controller 280 may be implemented as a singlecontroller or as multiple controllers. The controller 280 may beelectrically coupled to at least one component of a gas turbine engine.The controller 280 may control the temperature of heating element 210based upon an operating condition of the gas turbine engine to maintainblade tip clearance gap G. In various embodiments, controller 280 maycontrol the temperature of heating element 210 based upon variousoperating conditions or states, including altitude, throttle position,rotor speed, and bleed pressure, among others.

In various embodiments, heating element 210 may cause outer structure220 to increase in temperature via resistive heating using thermalconduction (interface heat transfer). Thus, heating element 210 mayincrease in temperature in response to an electrical current beingpassed there through, for instance a resistive heating element (e.g.,Joule heating). In this regard, electric power source 205 may provideelectric power to heating element 210, wherein in response to theelectric power, heating element 210 increases in temperature andconductively transfers thermal energy to outer structure 220.

In various embodiments, with particular focus on FIG. 2C, heatingelement 210 may cause outer structure 220 to heat up via inductionheating. Electric power source 205 may be configured to send alternatingcurrent (AC) to heating element 210, wherein in response to receivingthe alternating current there through, an electric field, illustrated bylines at 204, is generated by heating element 210. The electric field204 may penetrate outer structure 220, generating electric currentsinside outer structure 220, referred to as eddy currents. The eddycurrents, illustrated by lines at 206, flowing through outer structure220 cause outer structure 220 to heat by Joule heating. Although, heatmay also be generated by magnetic hysteresis losses. In this regard,heating element 210 may comprise an electromagnet. Heating element 210may be made from an electrically conducting material, such as copper forexample. Outer structure 220 may be made from an electrically conductingmaterial, including metals such as iron, or an iron alloy, among others.Outer structure 220 may be made from a ferromagnetic material, such asiron for example.

Heating element 210 may cause outer structure 220 to heat up viainduction heating when heating element 210 is in contact with outerstructure 220 (see FIG. 2A and FIG. 2B) or when heating element 210 isspaced apart from outer structure 220 (see FIG. 2C).

In various embodiments, heating element 210 may comprise a wire, a coil,a hollow tube, a plate, or any other suitable heating element for Jouleheating and/or induction heating.

In various embodiments, heating element 210 may be powered after engineshutdown in order to prevent adverse effects caused by rotor bow incompressor section 124. Stated differently, heating element 210 may bepowered after engine shutdown in order to prevent gap G from closing.Rotor bow, or thermal bowing, is typically due to asymmetrical coolingafter shut-down on a previous flight. Differences in temperature acrossa shaft section, e.g. low speed spool 130 and/or high speed spool 132the gas turbine engine supporting the rotor may lead to differentthermal deformation of the shaft material, causing the rotor axis tobend. This results in an offset between the center of gravity of thebowed rotor and the bearing axis, causing a slight imbalance andpotentially reducing the tight clearance between the rotor blade tipsand the compressor wall, which can adversely affect engine performance.

In this regard, a method for controlling a heating element 210 for a gasturbine engine may include detecting, by controller 280, a shutdown ofgas turbine engine 120, sending, by controller 280, electrical currentto a heating element 210, and heating outer structure 220, via heatingelement 210, to maintain blade tip clearance gap G.

In accordance with various embodiments, in an active clearance control(ACC) system, air impinges on the turbine case when activated to cooland shrink the case diameter. This in turn reduces the diameter of thesegmented blade outer air seal assembly. The seal body in thisapplication is in segments to prevent thermal fighting between the sealand the turbine case to which the seal ultimately mounts to and which isa full hoop. The turbine case that comprises the full hoop structure iswhat controls the position of the blade outer air seal. Due to the massof the turbine case and the thermal environment within which the turbinecase operates, the turbine case is slow to respond thermally as theengine power level is increased. The turbine rotor diameter, however,will increase rapidly as the rotational speed and temperature of theengine increases. For this reason, extra clearance may be added betweenthe tip of the blade and the blade outer air seal assembly to preventrubbing contact between these two structures. However, this extraclearance can adversely affect engine performance.

In various embodiments, the present disclosure provides a system andmethod for mitigating the desire for an ACC system to reduce clearancegap G. Outer structure 220 and rotor blade 262 may be configured suchthat under “cold” temperatures, e.g., during cruise, clearance gap G isminimal or at a desired dimension without the use of cooling air from anACC system. In this regard, extra clearance is not added duringmanufacturing between the tip of the rotor blade 262 and outer structure220. Rather, blade tip clearance G is configured to be optimal at cruiseconditions (“default closed”) and heating element 210 is used tomaintain clearance gap G in response to events that would otherwisecause blade tip strike, e.g. in response to a throttle acceleration.

In this regard, a method for controlling a heating element 210 for a gasturbine engine may include detecting, by controller 280, an increase inengine throttle of gas turbine engine 120, sending, by controller 280,electrical current to a heating element 210, and heating outer structure220, via heating element 210, to maintain blade tip clearance gap G.

With respect to FIG. 2D, elements with like element numbering, asdepicted in FIG. 2B, are intended to be the same and will notnecessarily be repeated for the sake of clarity.

With reference to FIG. 2D, a cross section axial view of clearancecontrol system 200B is illustrated in accordance with variousembodiments. In various embodiments, heating element 210 may be embeddedin outer structure 220, similar to FIG. 2B, and in various embodiments,heating element 210 may be coupled to the outer surface of outerstructure, similar to FIG. 2A, and in various embodiments, heatingelement 210 may be spaced apart from outer structure 220, similar toFIG. 2C. Outer structure 220 may define an engine centerline axis 290.Outer structure 220 may surround a plurality of rotor blades 262. Rotorblades 262 may rotate about engine centerline axis 290 with respect toouter structure 220.

With reference to FIG. 3A, clearance control system 300 may be locatedaboard an aircraft. Weight and packaging are factors when consideringdesign of a clearance control system for an aircraft. Furthermore,clearance control system 300 may require a substantial amount of powerin order to heat an outer structure, such as an engine case for example,to provide the thermal expansion desirable to maintain a blade tipclearance gap G. In this regard, a hybrid electric power source 305 isprovided for providing suitable power to clearance control system 300,in accordance with various embodiments. Hybrid electric power source 305may be capable of providing electric power on the order of kilowattsand/or megawatts of power to clearance control system 300 withoutdepriving the aircraft of electrical power required to operate all otherelectrical components aboard the aircraft or burdening the engine withadditional power offtake at moments when high engine thrust is required.

In various embodiments, hybrid electric power source 305 may compriseone or more batteries, one or more supercapacitors, one or moreultracapacitors, and/or one or more generators, or any other suitablepower source, such as a fuel cell for example.

Clearance control system 300 may include power electronic 358. Powerelectronics 358 may include any suitable power electronics for thecontrol and conditioning of electric power received from hybrid electricpower source 305 to heating element 310 and/or valve assembly 372. Forexample, power electronics 358 may include a bi-directional DC-DCconverter for energy storage charging and discharging, an AC-DCrectifier, e.g., a full bridge or a diode, a DC-AC inverter, a siliconecontrol rectifier (SCR), a pulse width modulated (PWM) controlledinverter, a pressure sensor, a temperature sensor, etc. Powerelectronics 358 may be in electronic communication with hybrid electricpower source 305 and an ACC control logic 370.

An injection source 373 may supply a cooling air flow 375 to outerstructure 320. The cooling air flow may be supplied from compressorsection 124, with momentary reference to FIG. 1. A conduit 374 may routethe cooling air flow 375 towards the outer surface 322 of outerstructure 320. A valve assembly 372 may be provided for metering thecooling air flow 375.

An ACC control logic 370 may coordinate the operation of the twosubsystems (i.e., heating element 310 and cooling air flow 375). Controllogic 370 may be implemented on a single processor or on separateprocessors. The cooling air flow contributes to shrinking the outerstructure 320 and therefore reduces blade tip clearance gap G. Becausethe heat transfer has a long time constant it may be desirable to usethe cooling air flow 375 subsystem in near steady-state operationconditions. In transient conditions it may be desirable toconservatively control the cooling air flow 375 to ensure that blade tipclearance gap G is maintained and that rotor blades 363 do not contactouter structure 320. As described, the electrical heating subsystem(i.e., heating element 310) has the opposite effect and leads to a morequick expansion of the outer structure 320. This effect may be desirablewhen there is potential for the turbomachinery clearances (blade tipclearance gap G) to decrease in a short duration of time, such as forexample, when the speed of rotor blades 362 increases abruptly, e.g.,increased throttle, and the mechanical growth of rotor blades 362exceeds the thermal growth of outer structure 320.

With respect to FIG. 3B, elements with like element numbering, asdepicted in FIG. 3A, are intended to be the same and will notnecessarily be repeated for the sake of clarity.

With reference to FIG. 3B, a clearance control system 301 isillustrated, in accordance with various embodiments. In variousembodiments, hybrid electric power source 305 may comprise one or morebatteries 306, one or more capacitors 307, and/or one or more generators308. In various embodiments, battery 306 may comprise any suitablebattery, such as a lithium-ion battery for example. Capacitor 307 maycomprise a supercapacitor or an ultracapacitor. In various embodiments,generator 308 may be an auxiliary generator driven by low speed spool130 or high speed spool 132, with momentary reference to FIG. 1. Anynumber of batteries 306, capacitors 307 and/or generators 308 may beprovided in any suitable arrangement (parallel, series) to provide theelectric power suitable for powering clearance control system 300.

In various embodiments, power electronics 358 may include a converter360. In various embodiments, converter 360 is a bidirectional converterfor energy storage charging and discharging. For example, generator 308may charge battery 306 and/or capacitor 307 via converter 360 inresponse to battery 306 and/or capacitor 307 being depleted ofelectrical energy. Furthermore, battery 306 may charge capacitor 307 viaconverter 360. In various embodiments, converter 360 is a DC/DCconverter for supplying DC power to heating element 310. Converter 360may supply power to heating element 310 via a DC bus 366. Converter 360may be in electronic communication with ACC control logic 370. Converter360 may directing energy to and/or from hybrid electric power source 305in response to commands received from ACC control logic 370.

In various embodiments, power electronics 358 may include a secondconverter 361. In various embodiments, second converter 361 may beprovided to control the electrical power provided to heating element310. In various embodiments, second converter 361 is a DC/DC converterfor converting DC power supplied from DC bus 366 to DC power for heatingelement 310 (e.g., for resistive heating). In various embodiments,second converter 361 is a DC/AC inverter for converting DC powersupplied from DC bus 366 to AC power for heating element 310 (e.g., forinduction heating). In various embodiments, second converter 361 is anAC/AC converter and/or a transformer for converting AC power suppliedfrom generator 308 to AC power for heating element 310 (e.g., forinduction heating). Second converter 361 may step up, or step down, thevoltage and/or current of the AC power, as well as vary the signalfrequency, based upon the desired AC power for heating element 310.

With reference to FIG. 3C, ACC control logic 370 logic may receiveinputs including source pressure P1 (i.e., pressure of cooling air flow375 upstream of valve assembly 372), sink pressure P2 (i.e., pressure ofcooling air flow 375 downstream of valve assembly 372), outer structuretemperature T (i.e., temperature of outer structure 320), a target bladetip clearance value (e.g., a desired blade tip clearance gap G), etc.One or more sensors may be used to measure the pressures of the coolingair flow, as well as any other inputs to ACC control logic 370. One ormore sensors may be used to measure the temperature of the outerstructure. ACC control logic 370 may utilized a constrained model-basedcontrol algorithm based upon known and/or measured parameters of the gasturbine engine to estimate the blade tip clearance gap G for supplyingcontrol signals to second converter 361 and valve assembly 372.

FIG. 4A illustrates an outer air seal assembly 60 spaced by a clearancegap G from a radially outer tip of a rotating blade 62. In variousembodiments, the blade 62 is a component of the turbine section 128 asshown in FIG. 1. However, the outer air seal assembly 60 may be used inother engine configurations and/or locations, for example in thecompressor sections. The outer air seal assembly 60 includes an outerair seal body 64 that is mounted to a clearance control ring 66. Aninternal cavity 68 is formed between an engine case 70 and the outer airseal assembly 60. A support structure 72 is associated with the enginecase 70 to provide support for the outer air seal assembly 60.

The subject disclosure provides a configuration where the clearancecontrol ring 66 is positioned adjacent the support structure 72 but isnot directly tied to the engine case 70 or support structure 72. Invarious embodiments, clearance control ring 66 may be formed as anannular ring. In one example configuration, the clearance control ring66 includes a first mount feature 74 and the seal body 64 includes asecond mount feature 76 that cooperates with the first mount feature 74such that the clearance control ring 66 can move within the internalcavity 68 independently of the support structure 72 and engine case 70in response to changes in temperature. In various embodiments, theclearance control ring 66 is a full hoop ring (i.e., annular) made froma material with a high thermal expansion coefficient, for example. Forexample, clearance control ring 66 may comprise a thermal expansioncoefficient that is greater than that of engine case 70. For example,with momentary reference to FIG. 6, in accordance with variousembodiments, clearance control ring 66 may grow (i.e., increase indiameter) in response to an increase in temperature and, in accordancewith various embodiments, clearance control ring 66 may shrink (i.e.,decrease in diameter) in response to a decrease in temperature.

With continued reference to FIG. 4A, in various embodiments, the sealbody 64 may include a ring mount portion 92. The clearance control ring66 is radially moveable relative to the first 84 and second 86 radialwall portions in response to temperature changes via the connectioninterface to the ring mount portion 92. A main seal portion 94 extendsfrom the ring mount portion 92 to face the blade 62.

In various embodiments, clearance control ring 66 may define a slot 98to receive ring mount portion 92. In the example shown, the clearancecontrol ring 66 includes the slot 98 and the seal body 64 includes thering mount portion 92; however, the reverse configuration could also beused. In various embodiments, the slot 98 and the ring mount portion 92comprise a key-shape, with each of the slot 98 and ring mount portion 92having a first portion extending in a radial direction and a secondportion extending in an axial direction. This type of configurationprovides a floating connection interface that fully supports andproperly locates the seal 64 while still controlling the seal 64 to moveradially inwardly and outwardly as needed.

With continued reference to FIG. 4A, clearance control ring 66 may besimilar to outer structure 220 of FIG. 2A, FIG. 2B, and/or FIG. 2C, inaccordance with various embodiments. A heating element 310 may beconfigured to cause clearance control ring 66 to vary in temperature tocause clearance control ring 66 to move radially (Y-direction) withininternal cavity 68 to maintain or vary clearance gap G. Heating element310 may be similar to heating element 210 of FIG. 1A, FIG. 1B, and/orFIG. 1C, in accordance with various embodiments. In the illustratedembodiment, heating element 310 is embedded in clearance control ring66; however, in various embodiments, heating element 310 may be coupledto an outer surface of clearance control ring 66, for instance similarto the illustrated embodiment of FIG. 2C, or may be spaced apart fromclearance control ring 66, for instance similar to the illustratedembodiment of FIG. 2C. Control 80 may control the supply of electricalcurrent from one or more power supplies 405 to heating element 310.

The illustrated configuration with the clearance control ring 66 mayreact faster than prior active control systems due to the reducedthermal mass and due to being exposed to air from the engine gaspath incontrast to prior systems where the heavy turbine case was exposed tothe engine core compartment temperatures.

With reference to FIG. 4B, an injection source 78 may inject or delivercooling fluid flow, for example, air flow, into the internal cavity 68to control a temperature of the clearance control ring 66 to allow theouter air seal body 64 to move in a desired direction to maintain adesired clearance between the outer air seal body 64 and a tip of theblade 62, i.e. to control the size of the clearance gap G. In oneexample, the injection source 78 comprises a tube or conduit 78 a thatreceives air flow from the compressor section 124 (FIG. 1) of the gasturbine engine. As shown in FIG. 4B, a control 80 is configured todeliver the compressor air at a first temperature T1 into the internalcavity 68 and against the clearance control ring 66 to allow the outerair seal body 64 to move in a first direction to maintain a desiredclearance during a first operating condition, and is configured todeliver compressor air at a second temperature T2 into the internalcavity 68 and against the outer air seal body 64 to allow the outer airseal body 64 to move in a second direction to maintain a desiredclearance during a second operating condition. In one example, the firstoperating condition comprises a takeoff or high load event, and thesecond operating condition comprises a descending event. In variousembodiments, the first operating condition comprises a first throttlesetting, and the second operating condition comprises a second throttlesetting, the first throttle setting being greater than the secondthrottle setting.

In these example operating conditions, the second temperature T2 is lessthan the first temperature T1. In this example, the compressor air atthe second temperature T2 can comprise cooled cooling air from thecompressor exit while the air at the first temperature can compriseuncooled compressor exit air. The control 80 comprises a microprocessorand/or control unit that is programmed to deliver air flow at the firstT1 or second T2 temperature as needed dependent upon the engineoperating condition. The control 80 may further include valves V, flowconduits, and/or heat exchangers as needed to deliver the compressor airat the desired temperature. The control 80 delivers higher temperatureair T1 into the cavity 68 when the clearance control ring 66 is toincrease in diameter and delivers lower temperature air T2 into thecavity 68 when the clearance control ring 66 is to decrease in diameter.It should be understood that while two different temperatures arediscussed as examples, the system is variable and the system can deliverfluid at any desired temperature.

The engine case 70 may include an opening 82 to receive the conduit 78 awhich directs compressor air into the cavity 68. The support structure72 includes a first radial wall portion 84 extending radially inwardfrom the engine case 70 and a second radial wall portion 86 axiallyspaced from the first radial portion 84 to define the internal cavity68. The opening 82 may be positioned axially between the first 84 andsecond 86 radial portions. The engine case 70 includes trenches orgrooves 88 adjacent to each of the first 84 and second 86 radial wallportions.

In various embodiments, heating element 310 may work in concert withinjection source 78 to maintain clearance gap G, enablingtwo-directional clearance control and tighter running clearances as aresult of smaller margins for maneuvers where outer seal assembly 60would otherwise be too slow to expand. Heat caused by heating element310 may cause outer seal body 64 to move in the radially outwarddirection (positive Y-direction, also referred to herein as a firstdirection). The cooling air flow supplied by injection source 78 maycause outer seal body 64 to move in the radially inward direction(negative Y-direction, also referred to herein as a second direction).

With respect to FIG. 5A and FIG. 5B, elements with like elementnumbering, as depicted in FIG. 4A and FIG. 4B, are intended to be thesame and will not necessarily be repeated for the sake of clarity.

FIG. 5A illustrates an outer air seal assembly 560 spaced by a clearancegap G from a radially outer tip of a rotating blade 62. In variousembodiments, the blade 62 is a component of the turbine section 128 asshown in FIG. 1. However, the outer air seal assembly 560 may be used inother engine configurations and/or locations, for example in thecompressor sections. The outer air seal assembly 560 includes an outerair seal body 564 that is mounted to a support structure 572. Thesupport structure 572 is associated with the engine case 570 to providesupport for the outer air seal assembly 560. The outer air seal body 564may be mounted to engine case 570 via support structure 572 and may movewith engine case 570 in response to changes in temperature.

Engine case 570 may be similar to outer structure 220 of FIG. 2A, FIG.2B, and/or FIG. 2C, in accordance with various embodiments. A heatingelement 510 may be configured to cause engine case 570 to vary intemperature to cause engine case 570 to move radially (Y-direction) tomaintain or vary clearance gap G. Heating element 510 may be similar toheating element 210 of FIG. 1A, FIG. 1B, and/or FIG. 1C, in accordancewith various embodiments. In the illustrated embodiment, heating element510 is coupled to a distal surface 574 of engine case 570; however, invarious embodiments, heating element 510 may be coupled to the proximalsurface 576 of engine case 570, may be embedded in engine case 570, forinstance similar to the illustrated embodiment of FIG. 2B, or may bespaced apart from engine case 570, for instance similar to theillustrated embodiment of FIG. 2C. Control 580 may control the supply ofelectrical current from one or more power supplies 505 to heatingelement 80.

With reference to FIG. 5B, an injection source 578 may inject or delivercooling fluid flow, for example, air flow, onto distal surface 574 ofengine case 570 to cause the outer air seal body 564 to move in adesired direction to maintain a desired clearance between the outer airseal body 564 and a tip of the blade 62, i.e. to control the size of theclearance gap G. Injection source 578 may operate similarly as describedwith respect to injection source 78 of FIG. 3B. Stated differently,injection source 578 may be similar to injection source 78 of FIG. 3B,except that injection source 578 directs cooling fluid flow to enginecase 570, instead of a clearance control ring.

In various embodiments, heating element 510 may work in concert withinjection source 578 to maintain clearance gap G, enabling activebi-directional clearance control and tighter running clearances as aresult of smaller margins for maneuvers where outer air seal assembly560 would otherwise be too slow to expand. In this regard, withreference now to FIG. 3A, ACC control logic 370 may control bothelectrical current supplied to heating element 310 and the position ofvalve assembly 372 for controlling cooling air flow 375 for bothexpansion and contraction of outer structure 320. In this regard, theterm “bi-directional control” as used herein may refer to the control ofthe expansion and contraction of outer structure 320 (e.g., the enginecase and/or the clearance control ring).

With reference to FIG. 7, a method 700 for active bi-directional controlof an outer structure for blade tip clearance management is illustrated,in accordance with various embodiments. Method 700 includes sending afirst control signal to power electronics for varying electrical currentsupplied to a heating element to cause an outer structure to move in afirst radial direction (step 710). Method 700 includes sending a secondcontrol signal to a valve assembly for varying a cooling air flowsupplied to the outer structure to cause the outer structure to move ina second radial direction (step 720).

With combined reference to FIG. 3B and FIG. 7, step 710 may include mayinclude sending, by ACC control logic 370, the first control signal tosecond converter 361 to vary the blade tip clearance G. The firstcontrol signal may be any suitable control signal for controlling thepower output of second converter 361 (e.g., a voltage signal and/or acurrent signal).

Step 720 may include sending, by ACC control logic 370, a second controlsignal to valve assembly 372 to vary the blade tip clearance G. Thesecond control signal may be any suitable control signal for controllingthe position of valve assembly 372 (e.g., a voltage signal and/or acurrent signal) to vary the cooling air flow 375.

With additional reference to FIG. 8, in various embodiments, step 710and step 720 may include receiving, by ACC control logic 370, anelectrical current value currently being applied to heating element 310(see step 802). Step 710 and step 720 may include receiving, by ACCcontrol logic 370, a valve position of valve assembly 372 (e.g., open,closed, etc.) (step 804).

Step 710 and step 720 may include receiving, by ACC control logic 370,one or more state inputs (step 804). The state inputs may includevarious engine operating states or conditions. The state inputs mayinclude a temperature value of outer structure 320, at least onepressure value (e.g., pressure value P1 and/or pressure value P2),engine throttle position, rotor speed (e.g., rotational velocity ofrotor blades 362 (see FIG. 3A)), and/or altitude, among others. Invarious embodiments, a temperature sensor 324 may be in thermalcommunication with heating element 310 and/or outer structure 320whereby ACC control logic 370 may detect the temperature of outerstructure 320. In various embodiments, a first pressure sensor 378 mayme located upstream from valve assembly 372 and a second pressure sensor379 may be located downstream from valve assembly 372 whereby ACCcontrol logic 370 may detect pressure P1 and pressure P2, respectively.In various embodiments, the pressure values may be directly measured ormay be synthesized.

Step 710 and step 720 may include may include measuring, by ACC controllogic 370, the actual blade tip clearance gap (e.g., blade tip clearancegap G) (step 810). blade tip clearance gap G may be measured using anysuitable method. For example, blade tip clearance gap G may be measuredusing capacitive measurements between rotor blades 362 and outerstructure 320 with momentary reference to FIG. 3A. In variousembodiments, blade tip clearance gap G may be measured using X-raytechniques, among others.

Step 710 and step 720 may include may include estimating, by ACC controllogic 370, the actual blade tip clearance gap (e.g., blade tip clearancegap G) (step 810). The estimated blade tip clearance may be determinedusing any suitable method. For example, the estimated blade tipclearance may be determined based upon the electrical current currentlybeing applied to heating element 310, the valve position of valveassembly 372, and the state inputs.

Step 710 and step 720 may include receiving, by ACC control logic 370, atarget blade tip clearance value (step 812). The target blade tipclearance value may be a predetermined blade tip clearance value. Thetarget blade tip clearance value may be a desired blade tip clearance.In various embodiments, the first control signal is based upon theestimated blade tip clearance gap G. For example, the first controlsignal may be configured to adjust the power output of second converter361 to cause outer structure 320 to increase in temperature or decreasein temperature based upon a difference between the estimated blade tipclearance gap and the target blade tip clearance gap. Stateddifferently, ACC control logic 370 may be configured to adjust theelectrical current supplied to heating element 310 to minimize thedifference between the estimated blade tip clearance gap and the targetblade tip clearance gap.

In various embodiments, the first control signal is based upon themeasured blade tip clearance gap G. For example, the first controlsignal may be configured to adjust the power output of second converter361 to cause outer structure 320 to increase in temperature or decreasein temperature based upon a difference between the measured blade tipclearance gap and the target blade tip clearance gap. Stateddifferently, ACC control logic 370 may be configured to adjust theelectrical current supplied to heating element 310 to minimize thedifference between the measured blade tip clearance gap and the targetblade tip clearance gap.

In various embodiments, the second control signal is based upon theestimated blade tip clearance gap. For example, the second controlsignal may be configured to adjust a position of valve assembly 372(e.g., between an open position and a closed position) to cause outerstructure 320 to increase in temperature or decrease in temperaturebased upon a difference between the estimated blade tip clearance gapand the target blade tip clearance gap. Stated differently, ACC controllogic 370 may be configured to adjust the cooling air flow 375 suppliedouter structure 320 to minimize the difference between the estimatedblade tip clearance gap and the target blade tip clearance gap.

In various embodiments, the second control signal is based upon themeasured blade tip clearance gap. For example, the second control signalmay be configured to adjust a position of valve assembly 372 (e.g.,between an open position and a closed position) to cause outer structure320 to increase in temperature or decrease in temperature based upon adifference between the measured blade tip clearance gap and the targetblade tip clearance gap. Stated differently, ACC control logic 370 maybe configured to adjust the cooling air flow 375 supplied outerstructure 320 to minimize the difference between the measured blade tipclearance gap and the target blade tip clearance gap.

In various embodiments, step 710 and/or step 720 may include computingthe thermal power needed to be transferred to the outer structure, whiletaking into account the delays and constraints associated with heattransfer from both subsystems (i.e., heating element 310 and cooling airflow 375 (step 814). Computing the thermal power may be implementedusing various control methods. For example, the thermal power may becomputed using internal models of the turbomachinery clearance thatrepresent the transient response of the clearance to both inputs (i.e.,electrical current/voltage/PWM duty-cycle, and cold flow). The modelsmay use both estimated and measured parameters. The two inputs may becoordinated in order to track as closely as possible the targetclearance value (rapid expansion during rapid accelerations realized viaheating element, and slower contraction control via the cooling airflow). Control methods may include single-input single-output (SISO)methods. Various rules may be combined with the SISO method(s). Invarious embodiments, a single proportional-integral-derivative controllogic may use the error between the target clearance and the currentclearance (estimated or measured) for generating the control signalcommunicated to the power electronics module (e.g., for case expansion)or to the cold flow control valve (e.g., for case contraction). Invarious embodiments, a rule combined with two SISO loops may be used—onefor the power electronics module and one for the cold flow control. Therule may determine which loop is active, and the respective SISO logicdetermines the level of current/voltage/duty-cycle or the cold flowvalve control signal. Control methods may include multi-inputmulti-output (MIMO) control methods. MIMO methods may use an integratedmodel for outer structure radial displacement (contraction/expansion)capturing the dynamics from valve position to outer structurecontraction and power electronics signal to outer structure expansioninto a single model. MIMO methods may include nonlinear control methods.For example, switching-based control logic that select the activesubsystem and its corresponding control signal in the same design (withno additional rules). Constrained model-based control (e.g., currentlyimplemented in the full authority digital engine control (FADEC) forcontrolling other effectors) that in addition to dynamical system modelalso include constraints associated with valve current, heating elementcurrent and/or voltage, rates of expansion/contraction, etc. MIMOmethods may include predictive control that, at any time step, uses aprediction of the outer structure radial displacement levels over a fewfuture time steps. These methods may improve the clearance controlaccuracy by compensating for the effects of the delays associated withthe heat transfers.

In various embodiments, ACC control logic 370 may send a heating thermalpower command to converter control 364 (step 816). Converter control 364may compute and send the first control signal to converter 361 forvarying the electrical current supplied to heating element 310 to varythe heating thermal power applied to outer structure 320 (step 818). Invarious embodiments, converter control 363 may be implemented in ACCcontrol logic 370; for example, converter control 363 and ACC controllogic 370 may be implemented in a single processor. In variousembodiments, converter control 363 may be implemented separately fromACC control logic 370; for example, converter control 363 and ACCcontrol logic 370 may be implemented in separate processors.

In various embodiments, ACC control logic 370 may send a cooling thermalpower command to valve control 376 (step 820). Valve control 376 maycompute and send the second control signal to valve assembly 372 (e.g.,to a solenoid) for varying the cooling air flow 375 supplied to outerstructure 320 to vary the cooling thermal power applied to outerstructure 320 (step 822). In various embodiments, valve control 376 maybe implemented in ACC control logic 370; for example, valve control 376and ACC control logic 370 may be implemented in a single processor. Invarious embodiments, valve control 376 may be implemented separatelyfrom ACC control logic 370; for example, converter control 363 and ACCcontrol logic 370 may be implemented in separate processors.

Benefits, other advantages, and solutions to problems have beendescribed herein with regard to specific embodiments. Furthermore, theconnecting lines shown in the various figures contained herein areintended to represent exemplary functional relationships and/or physicalcouplings between the various elements. It should be noted that manyalternative or additional functional relationships or physicalconnections may be present in a practical system. However, the benefits,advantages, solutions to problems, and any elements that may cause anybenefit, advantage, or solution to occur or become more pronounced arenot to be construed as critical, required, or essential features orelements of the disclosures. The scope of the disclosures is accordinglyto be limited by nothing other than the appended claims and their legalequivalents, in which reference to an element in the singular is notintended to mean “one and only one” unless explicitly so stated, butrather “one or more.” Moreover, where a phrase similar to “at least oneof A, B, or C” is used in the claims, it is intended that the phrase beinterpreted to mean that A alone may be present in an embodiment, Balone may be present in an embodiment, C alone may be present in anembodiment, or that any combination of the elements A, B and C may bepresent in a single embodiment; for example, A and B, A and C, B and C,or A and B and C.

Systems, methods and apparatus are provided herein. In the detaileddescription herein, references to “various embodiments”, “oneembodiment”, “an embodiment”, “an example embodiment”, etc., indicatethat the embodiment described may include a particular feature,structure, or characteristic, but every embodiment may not necessarilyinclude the particular feature, structure, or characteristic. Moreover,such phrases are not necessarily referring to the same embodiment.Further, when a particular feature, structure, or characteristic isdescribed in connection with an embodiment, it is submitted that it iswithin the knowledge of one skilled in the art to affect such feature,structure, or characteristic in connection with other embodimentswhether or not explicitly described. After reading the description, itwill be apparent to one skilled in the relevant art(s) how to implementthe disclosure in alternative embodiments.

Furthermore, no element, component, or method step in the presentdisclosure is intended to be dedicated to the public regardless ofwhether the element, component, or method step is explicitly recited inthe claims. No claim element is intended to invoke 35 U.S.C. 112(f)unless the element is expressly recited using the phrase “means for.” Asused herein, the terms “comprises”, “comprising”, or any other variationthereof, are intended to cover a non-exclusive inclusion, such that aprocess, method, article, or apparatus that comprises a list of elementsdoes not include only those elements but may include other elements notexpressly listed or inherent to such process, method, article, orapparatus.

What is claimed is:
 1. A hybrid energy storage and control system for aclearance control system for a gas turbine engine, comprising: a hybridelectric power source; a first converter; a second converter configuredto receive electric power from the hybrid electric power source via thefirst converter and configured to send the electric power to a heatingelement for controlling a blade tip clearance between a rotor blade andan outer structure of the gas turbine engine; and a controller inelectronic communication with the second converter.
 2. The hybrid energystorage and control system of claim 1, wherein the hybrid electric powersource comprises at least one of a battery, a supercapacitor, and anultracapacitor.
 3. The hybrid energy storage and control system of claim2, wherein the controller is configured to regulate the electric powersupplied to the heating element via the second converter.
 4. The hybridenergy storage and control system of claim 3, wherein the firstconverter is configured to regulate power between at least one of thebattery, the supercapacitor, and the ultracapacitor.
 5. The hybridenergy storage and control system of claim 4, wherein the secondconverter comprises a DC-DC converter, the heating element configured toheat up the outer structure by resistive heating.
 6. The hybrid energystorage and control system of claim 4, wherein the second convertercomprises a DC-AC inverter, the heating element configured to heat upthe outer structure by induction heating.
 7. The hybrid energy storageand control system of claim 4, wherein the second converter comprises aAC-AC converter, the heating element configured to heat up the outerstructure by induction heating.
 8. The hybrid energy storage and controlsystem of claim 4, wherein at least one of the battery, thesupercapacitor, and the ultracapacitor is configured to receive electricpower from a generator in response to the at least one of the battery,the supercapacitor, and the ultracapacitor being depleted of electricpower by the heating element.